1. Field of the Invention
The present invention relates to a linear positioning device for moving a tool or other load to selected predetermined positions.
2. Description of the Prior Art
The use of a relatively long-stroke master hydraulic cylinder operated by relatively high pressure and a servo control system including a train of additive, short-stroke pneumatic cylinders operated by a relatively low pressure to control the stroking of the master cylinder and thus the variable positions of a tool or other controlled load is known. Such a prior positioning apparatus is shown, for example, in U.S. Pat. No. 3,361,034. Positioners of this type have inherent advantages in compactness, simplicity and accuracy as compared to other, more conventional types of positioning setworks.
Nevertheless, such prior positioners commonly include as part of the servo control, in addition to the pneumatic control cylinder train, a complex combination of pneumatic, electrical, mechanical and hydraulic components which are exceedingly difficult for plant maintenance personnel to understand and thus service. Such complexities have also effected adversely the accuracy and dependability of prior such positioners.
Another shortcoming of prior such positioners is the lack of any built-in safeguard to prevent operation of the positioner when the controlled tool is in an operating or other condition under which movement could damage the tool, workpiece or positioning apparatus.
Accordingly there us a need for an improved linear positioner of the general type utilizing a master hydraulic positioning cylinder and a train of pneumatic servo control cylinders which eliminates or at least minimizes the foregoing deficiencies of prior such positioners.